U.S. patent application number 11/340643 was filed with the patent office on 2007-01-04 for operation method of nuclear power plant.
Invention is credited to Motoo Aoyama, Masao Chaki, Kazuaki Kitou, Masaya Ootsuka, Kouji Shiina.
Application Number | 20070000250 11/340643 |
Document ID | / |
Family ID | 37587922 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070000250 |
Kind Code |
A1 |
Chaki; Masao ; et
al. |
January 4, 2007 |
Operation method of nuclear power plant
Abstract
A nuclear power plant and an operation method of the nuclear
power plant, which can uprate plant power without greatly modifying
the construction of plant equipment, while keeping a core's
pressure loss characteristic, a safety margin, and a design margin
in the transient state substantially the same as those before the
power uprate. Thermal power in a second operation cycle of a
nuclear reactor is uprated from thermal power in a first operation
cycle preceding the second operation cycle at least one operation
cycle. A proportion of steam extracted from a steam system and
introduced to a feedwater heater, which is in particular extracted
from an intermediate point and an outlet of a high pressure
turbine, with respect to a flow rate of main steam is reduced in
the second operation cycle from that in the first operation cycle
such that temperature of feedwater discharged from the feedwater
heater lowers in the range of 1.degree. C. to 40.degree. C. in the
second operation cycle.
Inventors: |
Chaki; Masao; (Hitachi,
JP) ; Kitou; Kazuaki; (Tokai, JP) ; Aoyama;
Motoo; (Mito, JP) ; Ootsuka; Masaya; (Mito,
JP) ; Shiina; Kouji; (Mito, JP) |
Correspondence
Address: |
MATTINGLY, STANGER, MALUR & BRUNDIDGE, P.C.
1800 DIAGONAL ROAD
SUITE 370
ALEXANDRIA
VA
22314
US
|
Family ID: |
37587922 |
Appl. No.: |
11/340643 |
Filed: |
January 27, 2006 |
Current U.S.
Class: |
60/644.1 |
Current CPC
Class: |
G21D 1/02 20130101; Y02E
30/00 20130101; Y02E 30/30 20130101; G21D 3/00 20130101; G21C 1/084
20130101 |
Class at
Publication: |
060/644.1 |
International
Class: |
G21D 5/00 20060101
G21D005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 2005 |
JP |
2005-021835 |
Mar 10, 2005 |
JP |
2005-066498 |
Claims
1. An operation method of a nuclear power plant comprising: a
nuclear reactor; a high pressure steam system supplied with steam
generated in said nuclear reactor and extending from an outlet of
said nuclear reactor to an inlet of a low pressure turbine via a
high pressure turbine; a low pressure steam system extending from
the inlet of said low pressure turbine to an inlet of a condenser
for condensing the steam discharged from said low pressure turbine;
and a feedwater system including a feedwater heater for heating
feedwater supplied from said condenser and introducing the
feedwater discharged from said feedwater heater to said nuclear
reactor, the operation method comprising the steps of: uprating
second nuclear thermal power in a second operation cycle of said
nuclear reactor from first nuclear thermal power in a first
operation cycle before the second operation cycle; and reducing a
proportion of a mass flow rate of steam extracted from said high
pressure steam system and introduced to said feedwater heater in
the second operation cycle with respect to a mass flow rate of main
steam at the outlet of said nuclear reactor in comparison with a
proportion of a mass flow rate of steam extracted from said high
pressure steam system and introduced to said feedwater heater in
the first operation cycle with respect to the mass flow rate of
main steam at the outlet of said nuclear reactor, such that
temperature of the feedwater discharged from said feedwater heater
lowers in the range of 1.degree. C. to 40.degree. C. in the second
operation cycle from the feedwater temperature in the first
operation cycle.
2. An operation method of a nuclear power plant comprising: a
nuclear reactor; a high pressure steam system supplied with steam
generated in said nuclear reactor and extending from an outlet of
said nuclear reactor to an inlet of a low pressure turbine via a
high pressure turbine; a low pressure steam system extending from
the inlet of said low pressure turbine to an inlet of a condenser
for condensing the steam discharged from said low pressure turbine;
and a feedwater system including a feedwater heater for heating
feedwater supplied from said condenser and introducing the
feedwater discharged from said feedwater heater to said nuclear
reactor, the operation method comprising the steps of: uprating
second nuclear thermal power in a second operation cycle of said
nuclear reactor from first nuclear thermal power in a first
operation cycle before the second operation cycle; and reducing a
proportion of a mass flow rate of steam extracted from each of said
high pressure steam system and said low pressure steam system and
introduced to said feedwater heater in the second operation cycle
with respect to a mass flow rate of main steam at the outlet of
said nuclear reactor in comparison with a proportion of a mass flow
rate of steam extracted from each of said high pressure steam
system and said low pressure steam system and introduced to said
feedwater heater in the first operation cycle with respect to the
mass flow rate of main steam at the outlet of said nuclear reactor,
and setting a decrease of the proportion of the mass flow rate of
steam extracted from said high pressure steam system in the second
operation cycle with respect to the mass flow rate of main steam at
the outlet of said nuclear reactor from the proportion in the first
operation cycle to be larger than a decrease of the proportion of
the mass flow rate of steam extracted from said low pressure steam
system in the second operation cycle with respect to the mass flow
rate of main steam at the outlet of said nuclear reactor from the
proportion in the first operation cycle, such that temperature of
the feedwater discharged from said feedwater heater lowers in the
range of 1.degree. C. to 40.degree. C. in the second operation
cycle from the feedwater temperature in the first operation
cycle.
3. An operation method of a nuclear power plant comprising: a
nuclear reactor; a high pressure steam system supplied with steam
generated in said nuclear reactor and extending from an outlet of
said nuclear reactor to an inlet of a low pressure turbine via a
high pressure turbine; a low pressure steam system extending from
the inlet of said low pressure turbine to an inlet of a condenser
for condensing the steam discharged from said low pressure turbine;
and a feedwater system including a feedwater heater for heating
feedwater supplied from said condenser and introducing the
feedwater discharged from said feedwater heater to said nuclear
reactor, the operation method comprising the steps of: uprating
second nuclear thermal power in a second operation cycle of said
nuclear reactor from first nuclear thermal power in a first
operation cycle before the second operation cycle; and reducing a
mass flow rate of steam extracted from said high pressure steam
system and introduced to said feedwater heater in the second
operation cycle in comparison with a proportion of a mass flow rate
of steam extracted from said high pressure steam system and
introduced to said feedwater heater in the first operation cycle,
such that temperature of the feedwater discharged from said
feedwater heater lowers in the range of 1.degree. C. to 40.degree.
C. in the second operation cycle from the feedwater temperature in
the first operation cycle.
4. An operation method of a nuclear power plant comprising: a
nuclear reactor; a high pressure steam system supplied with steam
generated in said nuclear reactor and extending from an outlet of
said nuclear reactor to an inlet of a low pressure turbine via a
high pressure turbine; a low pressure steam system extending from
the inlet of said low pressure turbine to an inlet of a condenser
for condensing the steam discharged from said low pressure turbine;
and a feedwater system including a feedwater heater for heating
feedwater supplied from said condenser and introducing the
feedwater discharged from said feedwater heater to said nuclear
reactor, the operation method comprising the steps of: uprating
second nuclear thermal power in a second operation cycle of said
nuclear reactor from first nuclear thermal power in a first
operation cycle before the second operation cycle; and reducing a
mass flow rate of steam extracted from each of said high pressure
steam system and said low pressure steam system and introduced to
said feedwater heater in the second operation cycle in comparison
with a proportion of a mass flow rate of steam extracted from each
of said high pressure steam system and said low pressure steam
system and introduced to said feedwater heater in the first
operation cycle, and setting a decrease of the mass flow rate of
steam extracted from said high pressure steam system in the second
operation cycle from the mass flow rate of the extracted steam in
the first operation cycle to be larger than a decrease of the mass
flow rate of steam extracted from said low pressure steam system in
the second operation cycle from the mass flow rate of the extracted
steam in the first operation cycle, such that temperature of the
feedwater discharged from said feedwater heater lowers in the range
of 1.degree. C. to 40.degree. C. in the second operation cycle from
the feedwater temperature in the first operation cycle.
5. An operation method of a nuclear power plant comprising: a
nuclear reactor; a steam system including a high pressure steam
system and a low pressure steam system, which are supplied with
steam generated in said nuclear reactor; a condenser for condensing
the steam discharged from said low pressure turbine; and a
feedwater system including a low pressure feedwater heater
installed downstream of said condenser and upstream of a main
feedwater pump and heating the feedwater supplied from said
condenser, and a high pressure feedwater heater installed
downstream of said main feedwater pump and upstream of the nuclear
reactor and introducing the feedwater discharged from said high
pressure feedwater heater to said nuclear reactor, the operation
method comprising the steps of: uprating second nuclear thermal
power in a second operation cycle of said nuclear reactor from
first nuclear thermal power in a first operation cycle before the
second operation cycle; and reducing a temperature rise obtained by
said high pressure feedwater heater in the second operation cycle
in comparison with a temperature rise obtained by said high
pressure feedwater heater in the first operation cycle, such that
temperature of the feedwater discharged from said high pressure
feedwater heater lowers in the range of 1.degree. C. to 40.degree.
C. in the second operation cycle from the feedwater temperature in
the first operation cycle.
6. An operation method of a nuclear power plant comprising: a
nuclear reactor; a steam system including a high pressure steam
system and a low pressure steam system, which are supplied with
steam generated in said nuclear reactor; a condenser for condensing
the steam discharged from said low pressure turbine; and a
feedwater system including a low pressure feedwater heater
installed downstream of said condenser and upstream of a main
feedwater pump and heating the feedwater supplied from said
condenser, and a high pressure feedwater heater installed
downstream of said main feedwater pump and upstream of the nuclear
reactor and introducing the feedwater discharged from said high
pressure feedwater heater to said nuclear reactor, the operation
method comprising the steps of: uprating second nuclear thermal
power in a second operation cycle of said nuclear reactor from
first nuclear thermal power in a first operation cycle before the
second operation cycle; and reducing a proportion of a temperature
rise obtained by said high pressure feedwater heater in the second
operation cycle with respect to a total temperature rise obtained
by said high pressure feedwater heater and said low pressure
feedwater heater in comparison with a proportion of a temperature
rise obtained by said high pressure feedwater heater in the first
operation cycle with respect to the total temperature rise obtained
by said high pressure feedwater heater and said low pressure
feedwater heater, such that temperature of the feedwater discharged
from said high pressure feedwater heater lowers in the range of
1.degree. C. to 40.degree. C. in the second operation cycle from
the feedwater temperature in the first operation cycle.
7. An operation method of a nuclear power plant comprising: a
nuclear reactor; a steam system including a high pressure steam
system and a low pressure steam system, which are supplied with
steam generated in said nuclear reactor, said steam system further
including at least one of a moisture separator, a moisture
separator and heater, and a moisture separator and reheater between
said high pressure steam system and said low pressure steam system;
a condenser for condensing the steam discharged from said low
pressure turbine; and a feedwater system including a pressure
feedwater heater for heating the feedwater supplied from said
condenser and introducing the feedwater discharged from said
feedwater heater to said nuclear reactor; and at least one high
pressure extraction line for extracting steam from an intermediate
point of said high pressure turbine and a point downstream of an
outlet of said high pressure turbine and upstream of an inlet of
one of said moisture separator, said moisture separator and heater,
and said moisture separator and reheater, and for introducing the
extracted steam to said feedwater heater, the operation method
comprising the steps of: uprating second nuclear thermal power in a
second operation cycle of said nuclear reactor from first nuclear
thermal power in a first operation cycle before the second
operation cycle; and in said at least one high pressure extraction
line through which the extracted steam flows in the first operation
cycle, stopping the flow of the extracted steam in the second
operation cycle or adjusting a flow rate of the extracted steam in
the second operation cycle by extracted flow adjusting means
disposed in said at least one high pressure extraction line, such
that temperature of the feedwater discharged from said feedwater
heater lowers in the range of 1.degree. C. to 40.degree. C. in the
second operation cycle from the feedwater temperature in the first
operation cycle.
8. An operation method of a nuclear power plant comprising: a steam
system including a high pressure turbine supplied with steam
generated by heat of a nuclear reactor and a lower pressure turbine
for introducing the steam discharged from said high pressure
turbine; a condenser for condensing the steam discharged from said
low pressure turbine; a feedwater system including a feedwater
heater for heating feedwater supplied from said condenser and
introducing the feedwater discharged from said feedwater heater to
said nuclear reactor; and a feedwater heater bypassing line for
extracting a part of the feedwater from an intermediate point of
the feedwater system and returning the extracted feedwater to said
feedwater system after bypassing at least one unit of said
feedwater heater, the operation method comprising the steps of:
uprating second nuclear thermal power in a second operation cycle
of said nuclear reactor from first nuclear thermal power in a first
operation cycle before the second operation cycle; and lowering
temperature of the feedwater discharged from said feedwater heater
in the range of 1.degree. C. to 40.degree. C. in the second
operation cycle from the feedwater temperature in the first
operation cycle.
9. The operation method of the nuclear power plant according to
claim 1, wherein the following formulae are satisfied;
0<A.ltoreq.5, and T2.ltoreq.T1-7.7.times.(Q2-Q1)/(4.5.times.W)
where temperature of the feedwater discharged from said feedwater
heater in the first operation cycle is T1 (.degree. C.),
temperature of the feedwater discharged from said feedwater heater
in the second operation cycle is T2 (.degree. C.), a core flow rate
of the feedwater flowing into said nuclear reactor in the second
operation cycle is W (kg/s), and a rate of the power uprate is A
(%).
10. The operation method of the nuclear power plant according to
claim 1, wherein the following formulae are satisfied;
5<A.ltoreq.10, and
T2.ltoreq.T1-7.7.times.(Q2.times.(A+95)/100-Q1)/(4.5.times.W) where
temperature of the feedwater discharged from said feedwater heater
in the first operation cycle is T1 (.degree. C.), temperature of
the feedwater discharged from said feedwater heater in the second
operation cycle is T2 (.degree. C.), a core flow rate of the
feedwater flowing into said nuclear reactor in the second operation
cycle is W (kg/s), and a rate of the power uprate is A (%).
11. The operation method of the nuclear power plant according to
claim 1, wherein the following formulae are satisfied;
10<A<30, and
T2.ltoreq.T1-7.7.times.(Q2.times.(A+90)/100-Q1)/(4.5.times.W) where
temperature of the feedwater discharged from said feedwater heater
in the first operation cycle is T1 (.degree. C.), temperature of
the feedwater discharged from said feedwater heater in the second
operation cycle is T2 (.degree. C.), a core flow rate of the
feedwater flowing into said nuclear reactor in the second operation
cycle is W (kg/s), and a rate of the power uprate is A (%).
12. The operation method of the nuclear power plant according to
claim 1, wherein the first operation cycle is an operation cycle
that is performed for the first time after installation of said
nuclear power plant, the second operation cycle is an operation
cycle after the first operation cycle, and at least one operation
cycle is interposed between the first operation cycle and the
second operation cycle.
13. A nuclear power plant comprising: a nuclear reactor; a steam
system including a high pressure turbine and a lower pressure
turbine, which are supplied with steam generated in said nuclear
reactor; a condenser for condensing the steam discharged from said
low pressure turbine; a plurality of feedwater heaters for heating
feedwater supplied from said condenser; at least one extraction
line for extracting the steam from said steam system and
introducing the extracted steam to corresponding one of said
feedwater heaters; a feedwater system for introducing the feedwater
from said condenser to said nuclear reactor via said feedwater
heaters; an extracted flow control valve disposed in said at least
one extraction line; a temperature sensor disposed in said
feedwater system at a point between adjacent two of said plurality
of feedwater heaters disposed in said feedwater system or at a
point downstream of one of said plurality of feedwater heaters
which is positioned most downstream; and an extracted flow
controller for outputting an opening request command for said
extracted flow control valve based on a measured value from said
temperature sensor and a set value of feedwater temperature, said
nuclear power plant being operated such that second nuclear thermal
power in a second operation cycle of said nuclear reactor is
uprated from first nuclear thermal power in a first operation cycle
before the second operation cycle, and second feedwater temperature
in the second operation cycle is made lower than first feedwater
temperature in the first operation cycle.
14. A nuclear power plant comprising: a nuclear reactor; a steam
system including a high pressure turbine and a lower pressure
turbine, which are supplied with steam generated in said nuclear
reactor; a condenser for condensing the steam discharged from said
low pressure turbine; a plurality of feedwater heaters for heating
feedwater supplied from said condenser; at least one extraction
line for extracting the steam from said steam system and
introducing the extracted steam to corresponding one of said
feedwater heaters; a feedwater system for introducing the feedwater
from said condenser to said nuclear reactor via said feedwater
heaters; an extracted flow control valve and an extraction flow
rate measuring meter disposed in said at least one extraction line;
and an extracted flow controller for outputting an opening request
command for said extracted flow control valve based on a measured
value from said extraction flow rate measuring meter and a set
value of a flow rate of the extracted steam, said nuclear power
plant being operated such that second nuclear thermal power in a
second operation cycle of said nuclear reactor is uprated from
first nuclear thermal power in a first operation cycle before the
second operation cycle, and second feedwater temperature in the
second operation cycle is made lower than first feedwater
temperature in the first operation cycle.
15. A nuclear power plant comprising: a nuclear reactor; a steam
system including a high pressure turbine and a lower pressure
turbine, which are supplied with steam generated in said nuclear
reactor; a condenser for condensing the steam discharged from said
low pressure turbine; a plurality of feedwater heaters for heating
feedwater supplied from said condenser; at least one extraction
line for extracting the steam from said steam system and
introducing the extracted steam to corresponding one of said
feedwater heaters; a feedwater system for introducing the feedwater
from said condenser to said nuclear reactor via said feedwater
heaters; an extracted flow control valve disposed in said at least
one extraction line; at least one main steam flow rate measuring
meter disposed in said steam system between said nuclear reactor
and said high pressure turbine; and an extracted flow controller
for outputting an opening request command for said extracted flow
control valve based on a measured value from said main steam flow
rate measuring meter and a set value of a flow rate of the main
steam, said nuclear power plant being operated such that second
nuclear thermal power in a second operation cycle of said nuclear
reactor is uprated from first nuclear thermal power in a first
operation cycle before the second operation cycle, and second
feedwater temperature in the second operation cycle is made lower
than first feedwater temperature in the first operation cycle.
16. A nuclear power plant comprising: a nuclear reactor; a steam
generator for generating steam by using, as a heat source, a
coolant heated by said nuclear reactor; a steam system including a
high pressure turbine and a lower pressure turbine, which are
supplied with the steam generated in said steam generator; a
condenser for condensing the steam discharged from said low
pressure turbine; a plurality of feedwater heaters for heating
feedwater supplied from said condenser; at least one extraction
line for extracting the steam from said steam system and
introducing the extracted steam to corresponding one of said
feedwater heaters; a feedwater system for introducing the feedwater
from said condenser to said nuclear reactor via said feedwater
heaters; an extracted flow control valve disposed in said at least
one extraction line; a temperature sensor disposed in said
feedwater system at a point between adjacent two of said plurality
of feedwater heaters disposed in said feedwater system or at a
point downstream of one of said plurality of feedwater heaters
which is positioned most downstream; and an extracted flow
controller for outputting an opening request command for said
extracted flow control valve based on a measured value from said
temperature sensor and a set value of feedwater temperature, said
nuclear power plant being operated such that second nuclear thermal
power in a second operation cycle of said nuclear reactor is
uprated from first nuclear thermal power in a first operation cycle
before the second operation cycle, and second feedwater temperature
in the second operation cycle is made lower than first feedwater
temperature in the first operation cycle.
17. A nuclear power plant comprising: a nuclear reactor; a steam
generator for generating steam by using, as a heat source, a
coolant heated by said nuclear reactor; a steam system including a
high pressure turbine and a lower pressure turbine, which are
supplied with the steam generated in said steam generator; a
condenser for condensing the steam discharged from said low
pressure turbine; a plurality of feedwater heaters for heating
feedwater supplied from said condenser; at least one extraction
line for extracting the steam from said steam system and
introducing the extracted steam to corresponding one of said
feedwater heaters; a feedwater system for introducing the feedwater
from said condenser to said nuclear reactor via said feedwater
heaters; an extracted flow control valve and an extraction flow
rate measuring meter disposed in said at least one extraction line;
and an extracted flow controller for outputting an opening request
command for said extracted flow control valve based on a measured
value from said extraction flow rate measuring meter and a set
value of a flow rate of the extracted steam, said nuclear power
plant being operated such that second nuclear thermal power in a
second operation cycle of said nuclear reactor is uprated from
first nuclear thermal power in a first operation cycle before the
second operation cycle, and second feedwater temperature in the
second operation cycle is made lower than first feedwater
temperature in the first operation cycle.
18. A nuclear power plant comprising: a nuclear reactor; a steam
generator for generating steam by using, as a heat source, a
coolant heated by said nuclear reactor; a steam system including a
high pressure turbine and a lower pressure turbine, which are
supplied with the steam generated in said steam generator; a
condenser for condensing the steam discharged from said low
pressure turbine; a plurality of feedwater heaters for heating
feedwater supplied from said condenser; at least one extraction
line for extracting the steam from said steam system and
introducing the extracted steam to corresponding one of said
feedwater heaters; a feedwater system for introducing the feedwater
from said condenser to said nuclear reactor via said feedwater
heaters; an extracted flow control valve disposed in said at least
one extraction line; at least one main steam flow rate measuring
meter disposed in said steam system between said nuclear reactor
and said high pressure turbine; and an extracted flow controller
for outputting an opening request command for said extracted flow
control valve based on a measured value from said main steam flow
rate measuring meter and a set value of a flow rate of the main
steam, said nuclear power plant being operated such that second
nuclear thermal power in a second operation cycle of said nuclear
reactor is uprated from first nuclear thermal power in a first
operation cycle before the second operation cycle, and second
feedwater temperature in the second operation cycle is made lower
than first feedwater temperature in the first operation cycle.
19. A nuclear power plant according to claim 13, wherein said
extraction line in which said extracted flow control valve is
disposed is an extraction line for extracting the steam from said
steam system at a point downstream of a steam inlet of said high
pressure turbine and upstream of a steam outlet of said low
pressure turbine.
20. A nuclear power plant according to claim 13, wherein the second
nuclear thermal power is larger than the first nuclear thermal
power in the range of not less than 2% to less than 5%.
21. A nuclear power plant according to claim 13, wherein the second
nuclear thermal power is larger than the first nuclear thermal
power in the range of 5% to 20%.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an operation method of a
nuclear power plant and to a nuclear power plant. More
particularly, the present invention relates to an operation method
of a nuclear power plant and to a nuclear power plant, which are
suitable for an uprate of normal operation power output of a
nuclear power plant.
[0003] 2. Description of the Related Art
[0004] In a newly constructed nuclear power plant, electric power
has hitherto been uprated, for example, by improving the fuel
makeup or the shape and makeup of a fuel assembly so as to increase
the flow rate of main steam at a core outlet.
[0005] Such related art is disclosed in Patent Document 1 (JP,A
9-264983).
SUMMARY OF THE INVENTION
[0006] When the above-mentioned related art is applied to the
existing nuclear power plant, the rate of core flow passing through
a reactor core is substantially the same as that before the power
uprate, while thermal power of the core is increased. In a boiling
water reactor (BWR), therefore, an average void rate (proportion of
steam with respect to the channel volume) in the core is increased.
Accordingly, the flow speed of a coolant is increased and so is a
pressure loss in the core. Also, with an increase in the amount of
steam generated in the core, a pressure loss in a water-steam
two-phase flow section is increased and a margin of core safety
tends to reduce. Further, an increase of the average void rate in
the core increases an amount of steam condensed in the so-called
pressure transient state where pressure rises, for example, when a
generator load is cut off, thus resulting in a larger amount of
decrease of the average void rate in the core. Generally, the
boiling water reactor has a negative void feedback coefficient so
that the reactor power reduces as the void rate increases. In the
pressure transient state, however, the average void rate in the
core is reduced and the reactor power is increased. Thus, the
related art has a possibility that, after the power uprate, the
amount of decrease of the average void rate in the core is
increased in the pressure transient state and a design margin for
pressure transient events is reduced.
[0007] Meanwhile, the flow rate of main steam is increased
substantially in proportion to an increase of the power uprate. The
increased flow rate of main steam reduces design margins of almost
all equipment, such as feedwater equipment including feedwater
piping, a feedwater heater, a feedwater pump, etc., pressure vessel
internals including a dryer, etc., a main steam line, a high
pressure turbine, a low pressure turbine, and a condenser. In a
usual nuclear power plant employing a boiling water reactor, the
high pressure turbine is one of the equipment with a possibility
that the design margin is first lost with the increase in the flow
rate of main steam. Also, in a nuclear power system other than the
boiling water reactor, a similar problem arises in a plant where
the design margin for the high pressure turbine is relatively
small. Accordingly, when the related art is applied to the existing
nuclear power plant, large-scaled improvement and replacement of
plant equipment are required. The increase in the flow rate of main
steam can be suppressed by lowering the feedwater temperature.
However, such a solution is not realistic for the reason that, if
the flow rate of steam extracted for heating the feedwater is
simply reduced as a whole, thermal efficiency is noticieably
deteriorated and the electric power is not increased in proportion
to the core thermal power output.
[0008] An object of the present invention is to provide an
operation method of a nuclear power plant, which can uprate plant
power without greatly modifying the construction of plant
equipment, while keeping a core's pressure loss characteristic, a
safety margin, and a design margin in the transient state
substantially the same as those before the power uprate.
[0009] To achieve the above object, according to one aspect of the
present invention, assuming that one operation cycle is defined as
a period from a time at which a nuclear power plant starts
operation to a time at which the nuclear power plant stops the
operation for fuel exchange, second reactor thermal power in a
second operation cycle of a nuclear reactor is uprated from first
reactor thermal power in a first operation cycle preceding the
second operation cycle at least one operation cycle, and a
proportion of steam extracted from a steam system and introduced to
a feedwater heater, which is in particular extracted from an
intermediate point of a high pressure turbine and an outlet thereof
(practically, some point in a section ranging from the outlet of
the high pressure turbine to an inlet of one of a moisture
separator, a moisture separator and heater, and a moisture
separator and reheater), with respect to a flow rate of main steam
is reduced in the second operation cycle from a proportion in the
first operation cycle such that temperature of feedwater discharged
from the feedwater heater lowers in the range of 1.degree. C. to
40.degree. C. in the second operation cycle.
[0010] To achieve the above object, according to another aspect of
the present invention, second reactor thermal power in a second
operation cycle of a nuclear reactor is uprated from first reactor
thermal power in a first operation cycle preceding the second
operation cycle at least one operation cycle, and a mass flow rate
of steam extracted from a steam system and introduced to a
feedwater heater, which is in particular extracted from an
intermediate point and an outlet of a high pressure turbine, is
reduced in the second operation cycle from a mass flow rate of
steam extracted in the first operation cycle such that temperature
of feedwater discharged from the feedwater heater lowers in the
range of 1.degree. C. to 40.degree. C. in the second operation
cycle.
[0011] To achieve the above object, according to still another
aspect of the present invention, second reactor thermal power in a
second operation cycle of a nuclear reactor is uprated from first
reactor thermal power in a first operation cycle preceding the
second operation cycle at least one operation cycle, and a
temperature rise in one of a plurality of feedwater heaters,
particularly a high pressure feedwater heater installed downstream
of a main feedwater pump, is reduced in the second operation cycle
such that temperature of feedwater discharged from the feedwater
heater lowers in the range of 1.degree. C. to 40.degree. C. in the
second operation cycle.
[0012] To achieve the above object, according to still another
aspect of the present invention, second reactor thermal power in a
second operation cycle of a nuclear reactor is uprated from first
reactor thermal power in a first operation cycle preceding the
second operation cycle at least one operation cycle, and at least
one of extraction lines for extracting steam from a steam system
and introducing the extracted steam to a feedwater heater, which is
in particular extended from an intermediate point and an outlet of
a high pressure turbine, is shut off such that temperature of
feedwater discharged from the feedwater heater lowers in the range
of 1.degree. C. to 40.degree. C. in the second operation cycle.
[0013] To achieve the above object, according to another aspect of
the present invention, second reactor thermal power (Q2) in a
second operation cycle of a nuclear reactor is uprated A % from
first reactor thermal power (Q1) in a first operation cycle
preceding the second operation cycle at least one operation cycle,
and a proportion of steam extracted from a steam system and
introduced to a feedwater heater, which is in particular extracted
from an intermediate point of a high pressure turbine and an outlet
thereof (practically, some point in a section ranging from the
outlet of the high pressure turbine to an inlet of one of a
moisture separator, a moisture separator and heater, and a moisture
separator and reheater), with respect to a flow rate of main steam
in the second operation cycle is kept equivalent to or reduced from
a proportion in the first operation cycle such that the following
formulae are satisfied; 0<A.ltoreq.5, and
T2.ltoreq.T1-7.7.times.(Q2-Q1)/(4.5.times.W) where temperature of
the feedwater discharged from the feedwater heater in the first
operation cycle is T1 (.degree. C.), temperature of the feedwater
discharged from the feedwater heater in the second operation cycle
is T2 (.degree. C.), and a core flow rate of the feedwater flowing
into the nuclear reactor in the second operation cycle is W
(kg/s).
[0014] To achieve the above object, according to another aspect of
the present invention, second reactor thermal power (Q2) in a
second operation cycle of a nuclear reactor is uprated A % from
first reactor thermal power (Q1) in a first operation cycle
preceding the second operation cycle at least one operation cycle,
and a proportion of steam extracted from a steam system and
introduced to a feedwater heater, which is in particular extracted
from an intermediate point of a high pressure turbine and an outlet
thereof (practically, some point in a section ranging from the
outlet of the high pressure turbine to an inlet of one of a
moisture separator, a moisture separator and heater, and a moisture
separator and reheater), with respect to a flow rate of main steam
in the second operation cycle is kept equivalent to or reduced from
a proportion in the first operation cycle such that the following
formulae are satisfied; 5<A.ltoreq.10, and
T1-40.ltoreq.T2.ltoreq.T1-7.7.times.(Q2.times.(A+95)/100-Q1)/(4.5.times.W-
) where temperature of the feedwater discharged from the feedwater
heater in the first operation cycle is T1 (.degree. C.),
temperature of the feedwater discharged from the feedwater heater
in the second operation cycle is T2 (.degree. C.), and a core flow
rate of the feedwater flowing into the nuclear reactor in the
second operation cycle is W (kg/s).
[0015] To achieve the above object, according to another aspect of
the present invention, second reactor thermal power (Q2) in a
second operation cycle of a nuclear reactor is uprated A % from
first reactor thermal power (Q1) in a first operation cycle
preceding the second operation cycle at least one operation cycle,
and a proportion of steam extracted from a steam system and
introduced to a feedwater heater, which is in particular extracted
from an intermediate point of a high pressure turbine and an outlet
thereof (practically, some point in a section ranging from the
outlet of the high pressure turbine to an inlet of one of a
moisture separator, a moisture separator and heater, and a moisture
separator and reheater), with respect to a flow rate of main steam
in the second operation cycle is kept equivalent to or reduced from
a proportion in the first operation cycle such that the following
formulae are satisfied; 10<A<30, and
T2.ltoreq.T1-7.7.times.(Q2.times.(A+90)/100-Q1)/(4.5.times.W) where
temperature of the feedwater discharged from the feedwater heater
in the first operation cycle is T1 (.degree. C.), temperature of
the feedwater discharged from the feedwater heater in the second
operation cycle is T2 (.degree. C.), and a core flow rate of the
feedwater flowing into the nuclear reactor in the second operation
cycle is W (kg/s).
[0016] To achieve the above object, according to still another
aspect of the present invention, a nuclear power plant comprises an
extracted flow control valve disposed in at least one extraction
line; a temperature sensor disposed in a feedwater system at a
point between adjacent two of a plurality of feedwater heaters
disposed in the feedwater system or at a point downstream of one of
the plurality of feedwater heaters which is positioned most
downstream; and an extracted flow controller for outputting an
opening request command for the extracted flow control valve based
on a measured value from the temperature sensor and a set value of
feedwater temperature, wherein the nuclear power plant is operated
such that second nuclear thermal power in a second operation cycle
of the nuclear reactor is uprated from first nuclear thermal power
in a first operation cycle before the second operation cycle, and
second feedwater temperature in the second operation cycle is made
lower than first feedwater temperature in the first operation
cycle.
[0017] Since the feedwater temperature can be adjusted to a set
value through control of the opening of the extracted flow control
valve, it is possible to suppress variations in the amount of power
generated during the power uprate operation of the nuclear power
plant.
[0018] To achieve the above object, according to still another
aspect of the present invention, a nuclear power plant comprises an
extracted flow control valve and an extraction flow rate measuring
meter disposed in at least one extraction line; and an extracted
flow controller for outputting an opening request command for the
extracted flow control valve based on a measured value from the
extraction flow rate measuring meter and a set value of a flow rate
of the extracted steam, wherein the nuclear power plant is operated
such that second nuclear thermal power in a second operation cycle
of the nuclear reactor is uprated from first nuclear thermal power
in a first operation cycle before the second operation cycle, and
second feedwater temperature in the second operation cycle is made
lower than first feedwater temperature in the first operation
cycle.
[0019] To achieve the above object, according to still another
aspect of the present invention, a nuclear power plant comprises an
extracted flow control valve disposed in at least one extraction
line; at least one main steam flow rate measuring meter disposed in
a steam system between the nuclear reactor and the high pressure
turbine; and an extracted flow controller for outputting an opening
request command for the extracted flow control valve based on a
measured value from the main steam flow rate measuring meter and a
set value of a flow rate of the main steam, wherein the nuclear
power plant is operated such that second nuclear thermal power in a
second operation cycle of the nuclear reactor is uprated from first
nuclear thermal power in a first operation cycle before the second
operation cycle, and second feedwater temperature in the second
operation cycle is made lower than first feedwater temperature in
the first operation cycle.
[0020] According to the present invention, in trying to uprate
power of the existing nuclear power plant, the power uprate of the
nuclear power plant can be realized without greatly modifying the
construction of the nuclear power plant, while keeping a core's
pressure loss characteristic, a safety margin, a thermal margin,
and a design margin in the transient state substantially the same
as those before the power uprate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is an overall schematic view showing the overall
construction of a boiling water reactor system according to a first
embodiment of the present invention along with heat balance
obtained by an operation method according to the first embodiment
of the present invention;
[0022] FIG. 2 is an overall schematic view showing heat balance in
the boiling water reactor system before power uprate;
[0023] FIG. 3 is an overall schematic view showing heat balance in
the boiling water reactor system when the known power uprate method
is applied;
[0024] FIG. 4 graphically shows the relationships of operation
cycle versus reactor thermal power, flow rate of main steam and
flow rate of extracted steam;
[0025] FIG. 5 graphically shows the relationships of operation
cycle versus reactor thermal power, flow rate of main steam and
flow rate of extracted steam;
[0026] FIG. 6 graphically shows the relationships of operation
cycle versus reactor thermal power, flow rate of main steam and
flow rate of extracted steam;
[0027] FIG. 7 is an overall schematic view showing the overall
construction of a boiling water reactor system equipped with a
moisture separator and heater or a moisture separator and
reheater;
[0028] FIG. 8 is a schematic view of a boiling water reactor power
plant according to a second embodiment of the present
invention;
[0029] FIG. 9 is a flowchart showing control logic in an extracted
flow rate controller shown in FIG. 8;
[0030] FIG. 10 is a schematic view of a boiling water reactor power
plant according to a third embodiment of the present invention;
[0031] FIG. 11 is a schematic view of a boiling water reactor power
plant according to a fourth embodiment of the present
invention;
[0032] FIG. 12 is a flowchart showing control logic in an extracted
flow rate controller shown in FIG. 11;
[0033] FIG. 13 is a schematic view of a boiling water reactor power
plant according to a fifth embodiment of the present invention;
[0034] FIG. 14 is a schematic view of a boiling water reactor power
plant according to a sixth embodiment of the present invention;
[0035] FIG. 15 is a flowchart showing control logic in an extracted
flow rate controller shown in FIG. 14;
[0036] FIG. 16 is a schematic view of a pressurized water reactor
power plant according to a seventh embodiment of the present
invention;
[0037] FIG. 17 is a schematic view of a pressurized water reactor
power plant according to an eighth embodiment of the present
invention;
[0038] FIG. 18 is a schematic view of a pressurized water reactor
power plant according to a ninth embodiment of the present
invention;
[0039] FIG. 19 is a schematic view of a pressurized water reactor
power plant according to a tenth embodiment of the present
invention; and
[0040] FIG. 20 is a schematic view of a pressurized water reactor
power plant according to an eleventh embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0041] A first embodiment represents the case where the present
invention is applied to a boiling water reactor system as one of
nuclear power plants.
[0042] The overall construction of the boiling water reactor system
according to this embodiment will be first described with reference
to FIG. 1.
[0043] In FIG. 1, reference numeral 1 denotes a reactor pressure
vessel. Recirculation pumps and jet pumps are installed outside and
inside the reactor pressure vessel 1 to regulate the rate of flow
passing through a core (i.e., a core flow rate). The reactor
pressure vessel 1 and its internals constitute a reactor 21, and
steam generated in the reactor 21 is supplied to a steam system 22.
The steam system 22 comprises a main steam line 2, a high pressure
turbine 3 and a low pressure turbine 5 connected to the main steam
line 2 in series, and a moisture separator 4 disposed between the
high pressure turbine 3 and the low pressure turbine 5. A section
including the high pressure turbine 3, which extends from a reactor
outlet to an inlet of the low pressure turbine 5, constitutes a
high pressure steam system 22A, and a section extending from the
inlet of the low pressure turbine 5 to an inlet of a condenser 6
constitutes a low pressure steam system 22B. The condenser 6
condenses steam discharged from the low pressure turbine 5. The
condensate condensed by the condenser 6 is supplied as feedwater to
a feedwater system 23. The feedwater system 23 heats the feedwater
and returns it to the reactor 21. The feedwater system 23 includes
a main feedwater pump 8, a low pressure feedwater heater 7
installed downstream of the condenser 6 and upstream of the main
feedwater pump 8 and heating the feedwater supplied from the
condenser 6, and a high pressure feedwater heater 9 installed
downstream of the main feedwater pump 8 and upstream of the reactor
21. The feedwater discharged from the high pressure feedwater
heater 9 is introduced to the reactor 21 via a feedwater line
24.
[0044] Extraction lines 25, 26, 27 and 28 for extracting steam from
the steam system 22 and introducing the extracted steam to the high
pressure feedwater heater 9 and the low pressure feedwater heater 7
are disposed between the steam system 22 and corresponding one of
the high pressure feedwater heater 9 and the low pressure feedwater
heater 7. The extraction line 25 extracts steam from an
intermediate point of the high pressure turbine 3 and introduces
the steam to the high pressure feedwater heater 9. The extraction
line 26 extracts steam from an outlet of the high pressure turbine
3 (actually some point downstream of the outlet of the high
pressure turbine 3 and upstream of an inlet of the moisture
separator 4) and introduces the steam to the high pressure
feedwater heater 9. The extraction line 27 extracts steam from an
intermediate point of the moisture separator 4 and introduces the
steam to the low pressure feedwater heater 7. The extraction line
28 extracts steam from an intermediate point of the low pressure
turbine 5 and introduces the steam to the low pressure feedwater
heater 7. An extraction line flow adjusting valve 10, i.e.,
extracted steam amount adjusting means for adjusting an extracted
steam amount introduced from the intermediate point of the high
pressure turbine 3 to the high pressure feedwater heater 9, is
disposed in the extraction line 25.
[0045] The operation method of the thus-constructed nuclear power
plant according to this embodiment will be described below. In
FIGS. 1, 2 and 3, to explain heat balances, the reactor thermal
power is represented by Q, the mass flow rate of water and steam is
represented by G, and the enthalpy of water and steam is
represented by H. The thermal power Q and the mass flow rate G are
expressed by ratios (%) relative to the reactor thermal power and
the steam flow rate at an outlet of a reactor pressure vessel,
respectively, when the reactor is in the state before power uprate
as shown in FIG. 2. The enthalpy is expressed by a numerical value
in units of (kJ/kg). Note that each embodiment of the present
invention represents the ordinary operation state and excludes the
startup and shutdown states, the transient state, the operation
state where the core thermal power is changed by moving a control
rod position in a core to change the control rod pattern etc., and
the operation state in the event of an accident.
[0046] In the heat balances shown in FIGS. 1-3, as mentioned above,
the thermal power Q and the mass flow rate G are expressed by
ratios (%) relative to the reactor thermal power and the steam flow
rate at the outlet of the reactor pressure vessel, respectively,
when the reactor is in the state before power uprate as shown in
FIG. 2. According to the operation method of this embodiment, as
seen from the heat balances shown in FIGS. 1-3, when second reactor
thermal power in a second operation cycle (FIG. 1) of the reactor
21 is uprated from first reactor thermal power (FIG. 2) in a first
operation cycle (FIG. 2) prior to the second operation cycle (i.e.,
Q=100.fwdarw.105), a proportion (13/100) of the mass flow rate
(G=3+10=13) of steam extracted from the high pressure steam system
22A in the second operation cycle with respect to the mass flow
rate (G=100) of main steam at the reactor outlet is reduced from a
proportion (19/100) of the mass flow rate (G=9+10=19) of steam
extracted from the high pressure steam system 22A and introduced to
the feedwater heater 9 in the first operation cycle with respect to
the mass flow rate (G=100) of main steam at the reactor outlet
(i.e., 19/100.fwdarw.13/100). Also, the temperature of the
feedwater discharged from the feedwater heater 9 is lowered in the
second operation cycle (H=832) from that in the first operation
cycle (H=924). As described later, an extent to which the feedwater
temperature is lowered in the second operation cycle from that in
the first operation cycle is in the range of 1.degree. C. to
40.degree. C. Incidentally, one operation cycle is a period from a
time at which the reactor operation is started up from the shutdown
state to a time at which the reactor operation is shut down for
fuel exchange. Further, the feedwater temperature is one measured
at the period of the rated operation (maximum power output
operation), but not the period of the partial power output
operation such as the process of starting up and shutting down, as
stated later.
[0047] Looking from another aspect, according to the operation
method of this embodiment, the mass flow rate (G=3+10=13) of steam
extracted from the high pressure steam system 22A is reduced
(G=19.fwdarw.13) in the second operation cycle (FIG. 1) from the
mass flow rate (G=9+10=19) of steam extracted from the high
pressure steam system 22A and introduced to the feedwater heater 9
in the first operation cycle (FIG. 2), and the temperature of the
feedwater discharged from the feedwater heater 9 is lowered in the
second operation cycle from that in the first operation cycle.
Alternatively, it can also be said that, by making a temperature
rise in the feedwater heater 9 during the second operation cycle
(FIG. 1) smaller than a temperature rise in the feedwater heater 9
during the first operation cycle (FIG. 2), the temperature of the
feedwater discharged from the feedwater heater 9 is lowered in the
second operation cycle (H=832) from that in the first operation
cycle (H=924).
[0048] The operation method of this embodiment will be described in
more detail below.
[0049] FIG. 4 graphically shows the relationships of operation
cycle versus reactor thermal power, flow rate of main steam (amount
of steam flowing from the reactor pressure vessel 1 to the main
steam line 2), and flow rate of extracted steam in this embodiment
as compared with the power uprate by the known method. Note that
one operation cycle is defined as a period from a time at which the
reactor operation is started up from the shutdown state to a time
at which the reactor operation is shut down for fuel exchange.
Further, the feedwater temperature is one measured at the period of
the rated operation (maximum power output operation), but not the
period of the partial power output operation such as the process of
starting up and shutting down, as stated later.
[0050] Of operation cycles shown in FIG. 4, the N-th operation
cycle represents a cycle before the power uprating method of the
present invention is applied. At that time, the reactor thermal
power is Q=100%. FIG. 2 shows one example of heat balance prior to
the power uprate. The (N+1)-th operation cycle represents a cycle
in which the reactor thermal power is uprated 5% to obtain Q=105%.
Means for uprating the reactor thermal power can be realized by
increasing the amount of withdrawal of a control rod in the
(N+1)-th operation cycle from that in the N-th operation cycle, or
by raising the rotation speed of the recirculation pump to increase
the core flow rate in the (N+1)-th operation cycle from that in the
N-th operation cycle, or by modifying the kind of a fuel assembly.
Also, because the temperature of the feedwater supplied to the
reactor pressure vessel 1 is lowered with application of the
present invention, it is expected that the reactor thermal power is
naturally uprated with coolant density feedback as a result of
lowering of the coolant temperature at a core inlet. In some plant,
the flow rate of the extracted steam and the flow rate of the main
steam are changed during one operation cycle as shown in FIG. 5.
FIG. 5 shows an example in which, in the (N+1)-th operation cycle,
the reactor thermal power is reduced midway one operation cycle
with a drop of core reactivity, whereupon the flow rate of the
extracted steam and the flow rate of the main steam are reduced
(coasted down). Other than the operation cycle shown in FIG. 5, the
reactor power is also temporarily reduced, for example, when the
amount of insertion of the control rod in the core is changed. For
those reasons, in this embodiment, the heat balance, the flow rate
of the extracted steam, the flow rate of the main steam, the core
flow rate, the feedwater temperature, the reactor thermal power,
the extent of heating of the feedwater, etc. are compared at an
operation point where the flow rate of the main steam is maximized
during the operation cycle, except for the startup and shutdown
states, the operation state where the core thermal power is changed
by operating the control rod, in the event of an accident or a
transient phenomenon, and the test operation. In other words, such
an operation point means a point where the reactor thermal power is
maximized during the operation cycle. Further, when the thermal
power is 100% in the (N-1)-th operation cycle, but the thermal
power is largely reduced from the rated power of 100% for some
reason in the N-th cycle as shown in FIG. 6, the (N-1)-th operation
cycle represents the cycle before the present invention is applied
(i.e., the first operation cycle), and the (N+1)-th operation cycle
represents the cycle in which the present invention is applied
(i.e., the second operation cycle).
[0051] When the reactor thermal power is uprated, the flow rate of
the feedwater has to be increased or the enthalpy difference of a
coolant between the inlet and the outlet of the reactor pressure
vessel has to be increased in order to remove heat that has
increased in amount corresponding to the power uprate. The known
power uprating method employs the former manner; namely it
increases the flow rate of the feedwater in proportion to the
reactor thermal power. An example of heat balance according to the
known power uprating method is shown in FIG. 3. As a result of the
known power uprating method, the flow rate of the main steam in the
(N+1)-th operation cycle is increased to 105% as shown in FIG. 4.
The present invention employs the latter manner; namely it
intentionally reduces the coolant enthalpy at the inlet of the
reactor pressure vessel, to thereby increase the enthalpy
difference between the inlet and the outlet of the reactor pressure
vessel. The coolant enthalpy at the inlet of the reactor pressure
vessel can be reduced by reducing the flow rate of extracted steam
from the steam system 22 and supplied to the feedwater heater 9.
However, if the flow rate of the extracted steam is simply reduced
as a whole, the thermal efficiency is largely reduced and the
amount of generated power cannot be so increased. Such a reduction
of the thermal efficiency can be suppressed by selectively reducing
the extraction of steam from the high pressure steam system 22A,
which is constituted by the section including the high pressure
turbine 3 and extending from the reactor outlet to the inlet of the
low pressure turbine 5. The reason is that the steam in the high
pressure steam system 22A has higher energy than the steam in the
low pressure steam system 22B, which is constituted by the section
extending from the inlet of the low pressure turbine 5 to the inlet
of the condenser 6, and a thermal loss is reduced by selectively
reducing the extraction of steam from the high pressure steam
system 22A, whereby the reduction of the thermal efficiency
resulting from the power uprate can be suppressed. To selectively
reduce the extraction of steam from a relatively high energy
portion in the high pressure steam system 22A and to suppress the
reduction of the thermal efficiency, in this embodiment, the flow
rate of steam extracted from an intermediate point of the high
pressure turbine 3 or the outlet of the high pressure turbine 3
(actually some point between the outlet of the high pressure
turbine 3 and the inlet of the moisture separator 4) is selectively
reduced so that the flow rate of steam flowing into the low
pressure turbine 5 is increased and the amount of generated power
is increased. A large part of the steam extracted from the
intermediate point of the high pressure turbine 3 or the outlet of
the high pressure turbine 3 is used in the high pressure feedwater
heater 9 installed downstream of the main feedwater pump 8. Looking
from another aspect, therefore, the power uprating method according
to the present invention can also be said as a method of reducing
the extent of adding the thermal energy to the feedwater in the
region downstream of the main feed water pump 8.
[0052] In a plant where the flow rate of steam extracted from the
intermediate point of the high pressure turbine 3 or the outlet of
the high pressure turbine 3 is originally small, the flow rate of
steam extracted from the low pressure turbine 5 has to be also
reduced in order to sufficiently lower the feedwater temperature.
Even when the present invention is applied to such a plant, a
certain effect can be obtained by reducing the flow rate of steam
extracted from the intermediate point of the high pressure turbine
3 or the outlet of the high pressure turbine 3 to a larger extent.
With this embodiment, in spite of increasing the reactor thermal
power by 5% as compared with the N-th operation cycle, the flow
rate of the main steam can be kept the same as that in the N-th
operation cycle. Because this embodiment is described in connection
with the ideal power uprating method, the flow rate of the main
steam is the same in both the N-th operation cycle and the (N+1)-th
operation cycle. However, the flow rate of the main steam is not
always required to be the same in those operation cycles, and the
flow rate of the main steam may be increased within the range of a
design margin of the equipment including the high pressure turbine
3.
[0053] When there are a plurality of extraction points usable to
reduce the flow rate of the extracted steam, i.e., when there are a
plurality of extraction points midway the high pressure turbine 3
or at the outlet of the high pressure turbine 3, a maximum effect
can be obtained by selecting the most upstream extraction point. In
such a case, while the extraction line flow adjusting valve 10 for
controlling the flow rate of the extracted steam may be disposed to
reduce the flow rate of the extracted steam, one or more of the
extraction lines may be completely closed as an alternative manner.
To close the extraction line, a shut-off valve is disposed midway
the extraction line, or the extraction line is plugged. When the
extraction line is completely closed, equipment for controlling the
flow rate of the extracted steam is not required and the operation
control is simplified. Whether to control the flow rate of the
extracted steam or completely close the extraction line depends on
the heat balance and the extent of power uprate in the plant. (In
the case where the flow rate of the extracted steam per extraction
line is too large, the feedwater temperature is excessively lowered
if the extraction line is completely closed. Therefore, the flow
rate of the extracted steam is adjusted in that case.)
[0054] According to this embodiment, even when the reactor thermal
power is uprated to increase the amount of power generated in the
nuclear power plant, increases of both the flow rate of the
feedwater and the flow rate of the main steam can be suppressed,
whereby an increase of burdens imposed on the feedwater line 24,
the main steam line 2, and the pressure vessel internals can be
suppressed. As compared with the case of simply reducing the flow
rate of the extracted steam as a whole, it is possible to suppress
decrease of the thermal efficiency and to obtain larger electric
power. Further, although the high pressure turbine 3 must be
usually replaced when power is uprated to a large extent by the
known power uprating method, this embodiment can provide a wider
power uprate range available without replacing the high pressure
turbine 3 than that provided by the known method.
[0055] With the operation method of this embodiment, the feedwater
temperature is lowered. The lowering of the feedwater temperature
lowers the coolant temperature at the core inlet and increase the
thermal margin of the core (corresponding to MCPR (Minimum Critical
Power Ratio) in BWR), thus resulting in an advantage of ensuring
higher safety than that obtained with the known power uprating
method. The conventional power uprate increases the core pressure
loss and reduces the safety margin if the same fuels are used. In
contrast, the power uprating method of the present invention lowers
the coolant temperature at the core inlet and reduces the void rate
and the absolute value of the void coefficient in the core.
Therefore, the core pressure loss is reduced and a reduction of the
safety margin of the core is suppressed. Further, the design margin
for the pressure rising transient state is increased with the
reduction of the void rate and the absolute value of the void
coefficient in the core.
[0056] Thus, the lowering of the feedwater temperature is effective
in suppressing the deterioration of core characteristics and the
reduction of the design margin in the boiling water reactor during
the power update operation. Generally, because feedwater
temperature control is not especially performed in the boiling
water reactor, the feedwater temperature may change to the extent
of smaller than 1.degree. C. even in the same boiling water reactor
and at the same core thermal power due to change of heat balance in
the entire plant, in particular temperature change of the coolant
(seawater in many cases) that is used to condense the steam by the
condenser 6 shown in FIG. 1. In this embodiment, an extent to which
the feedwater temperature is lowered is set to about 20.degree. C.
Regarding the extent to which the feedwater temperature should be
lowered to compensate for the deterioration of the core
characteristics in the power uprate operation, however, the effect
of this embodiment can be obtained with a significant result by
lowering the feedwater temperature by a value of not smaller than
1.degree. C. that corresponds to the magnitude at which the
feedwater temperature is changed in the ordinary operation. In
addition, when the feedwater enters the reactor pressure vessel 1,
it is mixed with water at the saturation temperature inside the
reactor. Accordingly, there is a temperature difference between the
feedwater line 24 and the pressure vessel 1. If the feedwater
temperature is too lowered, the temperature difference in such a
mixing area is increased, thus causing a risk that a design limit
is exceeded from the viewpoint of thermal fatigue. From this point
of view, a limit of the extent to which the feedwater temperature
should be lowered from the current operation temperature is
40.degree. C.
[0057] The reduction of the core pressure loss means that an
increase of loads imposed on the jet pump and the recirculation
pump, which are used for recirculation of the coolant, due to the
power uprate can also be suppressed. Further, since the amount of
increase in quantity of steam generated in the core is
comparatively smaller than that of the thermal power, an influence
upon the carry under caused by entrainment with the recirculation
water can also be kept small and the flow window can be easily
ensured even in the case of large power uprate.
[0058] Table 1, given below, shows the relationships among the
reactor thermal power, the flow rate of the main steam, the flow
rate of the extracted steam, and the enthalpy of the feedwater when
the power uprating method of this embodiment is applied to the
cases of uprating the power at various rates. Each value of the
reactor thermal power and the flow rate of the main steam
represents a ratio relative to that at 100% of the reactor thermal
power, and a value of the flow rate of the extracted steam
represents a ratio relative to the flow rate of the main steam at
100% of the reactor thermal power. As seen from Table 1, the power
uprating method of this embodiment can be applied over a wide range
including even the case where the reactor thermal power is uprated
to 110%. The reason why Table 1 shows only the power uprate up to
110% is that the power uprate in excess of 110% requires
replacement of the moisture separator 4. If the replacement of the
moisture separator 4 is allowed or a combination with, e.g., an
increase of the core pressure and/or with employment of a moisture
separator and reheater is considered, the power uprating method of
this embodiment can be applied over a wider range of power
uprate.
[0059] In the boiling water reactor, uprate of the reactor thermal
power up to about 102% is generally feasible just by increasing the
measurement accuracy of a feedwater flowmeter, etc. Therefore, the
present invention is more effective when applied to the case of
uprating the reactor thermal power in excess of 102%. Further, at
the power uprate up to about 105% of the reactor thermal power,
substantial change of system equipment, e.g., replacement of the
high pressure turbine 3, is not required in general. The effect of
this embodiment is especially noticeable when applied to the uprate
of the reactor thermal power in excess of 105% because the
replacement of the high pressure turbine 3 is not required even in
that case. TABLE-US-00001 TABLE 1 Reactor Flow rate of Enthalpy of
thermal power Flow rate of extracted feedwater (%) main steam (%)
steam (%) (kJ/kg) 100 100 45 924 103 100 43 869 105 100 42 831 107
100 40 795 110 100 38 739 110 105 42 831
[0060] In view of the above-mentioned fact that substantial change
of system equipment, e.g., replacement of the high pressure turbine
3, is not required in general at the ordinary power uprate up to
about 105% of the reactor thermal power, an application method of
this embodiment may be changed between the case of uprating the
reactor thermal power at a rate of not larger than 5% and the case
of uprating the reactor thermal power at a rate of larger than 5%.
More specifically, because the replacement of the high pressure
turbine 3 is not required when the increase rate of the reactor
thermal power is not larger than 5%, it is primarily intended to
keep the above-mentioned core characteristic (core average void
rate) the same as that before the power uprate. Assuming that the
reactor thermal power before the power uprate is Q1 (kW), the
reactor thermal power after the power uprate is Q2 (kW), and the
increase rate of the power uprate is A (%), the power uprate of not
larger than 5% is expressed by A.ltoreq.5. Also, on an assumption
that the core flow rate after the power uprate is W (kg/s), the
specific heat at constant pressure at about 200.degree. C. under 7
MPa, i.e., the operating pressure in a typical boiling water
reactor, is about 4.5 (kJ/kgK), and a proportion of the flow rate
of the feedwater with respect to the core flow rate in the typical
boiling water reactor is about 13%, the condition for keeping the
core average void rate the same as that before the power uprate is
given as follows.
[0061] Change in thermal value of the feedwater per 1.degree. C. of
the feedwater temperature is expressed by: W(kg/s).times.13 (%)/100
(%).times.4.5 (kJ/kgK)=W.times.13/100.times.4.5 (kW/K) Assuming
here that the feedwater temperature before the power uprate is T1
and the feedwater temperature after the power uprate is T2, the
feedwater temperature T2 required to reduce the thermal value of
the feedwater, which is equivalent to the thermal value (Q2-Q1)
(kW) corresponding to the power uprate, is determined by the
following equation:
Q2-Q1=W.times.13/100.times.4.5.times.(T1-T2)
[0062] In order to hold the core characteristics equivalent to or
better than those before the power uprate, the feedwater thermal
value is just required to be reduced by an amount of not smaller
than the thermal value increased with the power uprate. The
condition to meet such a requirement is expressed by:
Q2-Q1.ltoreq.W.times.13/100.times.4.5.times.(T1-T2) This formula is
rewritten into: T2.ltoreq.T1-7.7.times.(Q2-Q1)/(4.5.times.W) Stated
another way, by setting the feedwater temperature so as to satisfy
the above formula in the case of the power uprate of not larger
than 5%, the core characteristics, such as the thermal margin, the
pressure loss characteristic, the safety margin, and the design
margin in the transient state of the core, can be basically held
equivalent to or better than those before the power uprate.
Further, since the flow rate of the main steam is kept equivalent
to or reduced from that before the power uprate, the design margin
of the main steam system, including the high pressure turbine and
the dryer, can also be held equivalent to or better than those
before the power uprate.
[0063] A description is made of the feedwater temperature when the
nuclear thermal power is uprated at a rate of larger than 5%, but
not larger than 10%. When the nuclear thermal power is uprated at a
rate of larger than 5% by the known power uprating method, the flow
rate of the main steam is also increased in excess of 5%, thus
generally resulting in that the design margin of equipment, e.g.,
the high pressure turbine, is exceeded. Therefore, such equipment
has to be replaced. In that case, by lowering the feedwater
temperature as in this embodiment, the increase in the flow rate of
the main steam can be held not larger than 5%.
[0064] Assuming here that the increase in the flow rate of the main
steam up to 5% is allowed, a reduction of the feedwater thermal
value required when the power uprate is increased at A (%)
corresponds to the power increase of (A-5)% and is expressed by:
Q2.times.(A-5+100)/100-Q1=Q2.times.(A+95/100)-Q1 On the assumption
that the feedwater temperature before the power uprate is T1 and
the feedwater temperature after the power uprate is T2, the above
thermal value can be offset when T1 and T2 satisfy the following
formula:
Q2.times.(A+95/100)-Q1=W.times.13/100.times.4.5.times.(T1-T2) Thus,
the increase in the flow rate of the main steam can be held not
larger than 5% by satisfying:
Q2.times.(A+95/100)-Q1.ltoreq.W.times.13/100.times.4.5.times.(T1-T2)
With rewrite of this formula, T2 is expressed by:
T2.ltoreq.T1-7.7.times.(Q2.times.(A+95)/100)-Q1)/(4.5.times.W) In
the case of the power uprate being larger than 5%, but not larger
than 10%, therefore, if the feedwater temperature T2 satisfies the
above formula, the power uprate can be realized within the range of
the design margin of the high pressure turbine, etc. and the
replacement of such equipment is not required. Further, the design
margins of the high pressure turbine and the core can be held
equivalent to or larger than those resulting at the power uprate of
5% by the known method.
[0065] At the power uprate in excess of 10%, it is generally
required in the boiling water reactor to replace, e.g., the
moisture separator in addition to the high pressure turbine, etc.
This problem can be overcome by lowering the feedwater temperature
in a similar manner to hold the increase in the flow rate of the
main steam to be not larger than 10% so that the replacement of the
moisture separator is not required. The condition of meeting such a
requirement in this case is given as follows for the rate A (%) of
the power uprate based on the same concept as that when the power
uprate is larger than 5%, but not larger than 10%:
Q2.times.(A-10+100)/100-Q1.ltoreq.W.times.13/100.times.4.5.times.(T1-T2)
With rewrite of this formula, T2 is expressed by:
T2.ltoreq.T1-7.7.times.(Q2.times.(A+90)/100-Q1)/(4.5.times.W) This
indicates an extent of lowering of the feedwater temperature within
which the replacement of the moisture separator is not required at
the power uprate of larger than 10%. In that case, the design
margins of the high pressure turbine and the core can also be held
equivalent to or larger than those resulting at the power uprate of
10% by the known method.
[0066] At any of the power uprate of not larger than 5%, the power
uprate of larger than 5%, but not larger than 10%, and the power
uprate of larger than 10%, the extent of lowering of the feedwater
temperature in excess of 40.degree. C. is undesired in practice
from the viewpoint of thermal fatigue. Also, as the power uprate
increases, the thermal margin of the core is reduced. It can be
generally said that the thermal margin of the core is bearable for
the power uprate up to about 20% by employing new fuel. Another
conceivable solution is to improve, e.g., a pump for increasing the
core flow rate. Even in consideration of such an improvement as
well, the power uprate at a rate of about 30% is regarded to be a
limit from the viewpoint of the core characteristics. Further,
looking at the equipment side, the power uprate over 30% is also
not desired in practice because such large power uprate exceeds the
design limits of the low pressure turbine and the condenser, which
are more expensive than the high pressure turbine, and hence
requires replacement of those other units of equipment.
[0067] According to this embodiment, for the power uprate of not
larger than 5%, the power uprate can be realized while holding the
design margins of the high pressure turbine and the core equivalent
to or larger than those before the power uprate. For the power
uprate of larger than 5%, but not larger than 10%, the power uprate
can be realized up to 10% while holding the design margins of the
high pressure turbine and the core equivalent to or larger than
those resulting at the power uprate of 5% by the known method. For
the power uprate of larger than 10%, the power uprate can be
realized in excess of 10% with no need of replacing the moisture
separator, etc. while holding the design margins of the moisture
separator and the core equivalent to or larger than those resulting
at the power uprate of 10% by the known method.
[0068] The present invention can be modified in various ways
without being restricted to the above-described embodiment. For
example, in the boiling water reactor system, a moisture separator
and heater or a moisture separator and reheater 11, shown in FIG.
7, may be used instead of the moisture separator 4. Even in that
case, although a steam extraction line 31 and a drain line 32 are
added, the operation method of the present invention can be applied
as in the above-described embodiment and can provide similar
advantages without causing substantial change with regards to main
parameters, such as the feedwater temperature and the flow rate of
the main steam.
[0069] While the above embodiment is described as applying the
present invention to the boiling water reactor power plant, the
present invention is applicable to a pressurized water reactor
system as well.
Second Embodiment
[0070] Another embodiment of the present invention in which the
invention is applied to the boiling water reactor power plant as
one of nuclear power plants will be described below with reference
to FIGS. 8 and 9. The same components as those in the first
embodiment are denoted by the same numerals.
[0071] As in the first embodiment, he boiling water reactor power
plant of this embodiment comprises a reactor pressure vessel 1, a
main steam line 2, a high pressure turbine 3 and a low pressure
turbine 5 connected to the main steam line 2 in series, and a
moisture separator 4 (or a moisture separator and heater) disposed
in the main steam line 2 between the high pressure turbine 3 and
the low pressure turbine 5. A low pressure feedwater heater 7, a
feedwater pump 8, and a high pressure feedwater heater 9 are
installed in a feedwater system 23 downstream of a condenser 6.
[0072] When the reactor thermal power is uprated, the flow rate of
the feedwater has to be increased or the enthalpy difference of the
coolant between the inlet and the outlet of the reactor pressure
vessel 1 has to be increased in order to remove heat that has
increased in amount corresponding to the power uprate. The known
power uprating method employs the former manner; namely it
increases the flow rate of the feedwater in proportion to the
reactor thermal power. On the other hand, as a new power uprating
method, there is also proposed a method of suppressing increases of
both the flow rate of the main steam and the flow rate of the
feedwater in the power uprate operation based on the latter manner
by intentionally reducing the coolant enthalpy (temperature) at the
inlet of the reactor pressure vessel, to thereby increase the
enthalpy difference between the inlet and the outlet of the reactor
pressure vessel. This embodiment is adapted for such a new power
uprating method and requires additional equipment for widening a
feedwater temperature controllable range so that the feedwater
temperature is lowered to a value beyond the range estimated in the
stage of plant construction.
[0073] The necessity of widening the feedwater temperature
controllable range toward the lower temperature side in turn
requires the flow rate of steam extracted for heating the feedwater
to be reduced in comparison with that before the power uprate. The
steam extracted from the high pressure turbine 3 for heating the
feedwater is introduced to the high pressure feedwater heater 9 via
extraction lines 25 and 26. Also, the steam extracted from the low
pressure turbine 5 is sent to the low pressure feedwater heater 7
via an extraction line 28. An extracted flow control valve 38 is
disposed in the extraction line 25 to adjust the flow rate of the
extracted steam. In the boiling water reactor power plant of this
embodiment, a plurality of main extraction lines are installed
downstream of the inlet of the high pressure turbine and upstream
of the outlet of the low pressure turbine.
[0074] In the boiling water reactor power plant of this embodiment
to which the above-mentioned new power uprating method is applied,
it is important that the feedwater temperature be surely lowered to
a preset value. For that reason, a feedwater temperature sensor 39
is disposed in the feedwater system 23 downstream of the high
pressure feedwater heater 9 that is located most downstream in the
feedwater system 23. The feedwater temperature sensor 39 measures
the temperature of the feedwater discharged from the high pressure
feedwater heater 9 and outputs a feedwater temperature measured
value signal 41. An extracted flow controller 40 controls the
opening of the extracted flow control valve 38 to adjust the flow
rate of the extracted steam. The feedwater temperature sensor 39 is
disposed in the feedwater system 23 downstream of the high pressure
feedwater heater 9, to which the extracted steam is supplied at the
adjusted flow rate, and upstream of the inlet of the reactor
pressure vessel 1. Alternatively, the feedwater temperature sensor
39 may be disposed between the high pressure feedwater heater 9 and
another suitable feedwater heater installed downstream of the
former.
[0075] One example of control logic executed by the extracted flow
controller 40 in the second embodiment will be described below with
reference to FIG. 9. The extracted flow controller 40 receives the
feedwater temperature measured value signal 41 outputted from the
feedwater temperature sensor 39 and a feedwater temperature set
value signal 42. Based on the feedwater temperature measured value
signal 41 and the feedwater temperature set value signal 42, the
extracted flow controller 40 produces an opening demand signal 43
and outputs the opening demand signal 43 to the extracted flow
control valve 38. If the measured value of the feedwater
temperature is lower than the set value of the feedwater
temperature, this means that the flow rate of the extracted steam
is insufficient. Therefore, the extracted flow controller 40
outputs the opening demand signal 43 to increase the opening of the
extracted flow control valve 38. Conversely, if the measured value
of the feedwater temperature is higher than the set value, this
means that the flow rate of the extracted steam is too large.
Therefore, the extracted flow controller 40 outputs the demand
signal 43 to reduce the opening of the extracted flow control valve
38.
[0076] According to this embodiment, since the feedwater
temperature can be adjusted to the set value through control of the
opening of the extracted flow control valve 38, it is possible to
suppress variations in the amount of power generated during the
power uprate operation of the nuclear power plant.
[0077] Also, according to this embodiment, since the feedwater
temperature can be always held at the set value, it is possible to
suppress the increases of both the flow rate of the main steam and
the flow rate of the feedwater by lowering the feedwater
temperature in the power uprate operation of the reactor. Further,
since the feedwater temperature can be adjusted in real time, even
in the case of changing the thermal power of the nuclear power
plant, the operation method of this embodiment is adaptable for the
load following operation of the nuclear power plant by modifying
the set value of the feedwater temperature depending on the change
of the thermal power, while the flow rate of the main steam and the
flow rate of the feedwater are held constant.
Third Embodiment
[0078] A boiling water reactor power plant according to still
another embodiment (third embodiment) of the present invention will
be described below with reference to FIG. 10.
[0079] This third embodiment differs from the second embodiment in
that, instead of the feedwater temperature sensor 39, an extraction
flowmeter 44 is disposed in the extraction line 25 in which the
extracted flow control valve 38 is disposed. The extracted flow
controller 40 receives a measured value from the extraction
flowmeter 44 and a set value of the flow rate of the extracted
steam. The extraction flowmeter 44 measures the flow rate of the
extracted steam supplied to the high pressure feedwater heater 9.
The extracted flow control valve 38 and the extraction flowmeter 44
may be disposed in the extraction line 25 irrespective of which one
of them is positioned upstream of the other. When the extraction
line 25 is merged midway with another extraction line (e.g., the
extraction line 26), one of the extracted flow control valve 38 and
the extraction flowmeter 44, which is positioned on the downstream
side, may be disposed in the extraction line 25 downstream of the
merging point between the two extraction lines. Also, when the
extraction line 25 is branched midway, one of the extracted flow
control valve 38 and the extraction flowmeter 44, which is
positioned on the downstream side, may be disposed in a line after
being branched. If the reactor thermal power, the flow rate of the
feedwater, and the flow rate of the extracted steam are known, the
feedwater temperature is uniquely decided from the heat balance of
the nuclear power plant. Accordingly, measuring the flow rate of
the extracted steam by the extraction flowmeter 44 disposed in the
extraction line 25, as in this embodiment, is equivalent to
measurement of the feedwater temperature.
[0080] In this embodiment, the extracted flow controller 40
receives an extracted flow measured value signal 45 outputted from
the extraction flowmeter 44 and a set value signal 42A for the flow
rate of the extracted steam. Based on the extracted flow measured
value signal 45 and the extracted flow set value signal 42A, the
extracted flow controller 40 outputs an opening demand signal 43
for the extracted flow control valve 38. The opening of the
extracted flow control valve 38 is controlled in accordance with
the opening demand signal 43. If the measured value of the flow
rate of the extracted steam is smaller than the set value of the
flow rate of the extracted steam, this means that the flow rate of
the extracted steam is insufficient. Therefore, the extracted flow
controller 40 outputs the opening demand signal 43 to increase the
opening of the extracted flow control valve 38. Conversely, if the
measured value of the flow rate of the extracted steam is larger
than the set value, this means that the flow rate of the extracted
steam is too large. Therefore, the extracted flow controller 40
outputs the opening demand signal 43 to reduce the opening of the
extracted flow control valve 38. This third embodiment can also
provide similar advantages to those obtainable with the second
embodiment.
Fourth Embodiment
[0081] A boiling water reactor power plant according to still
another embodiment (fourth embodiment) of the present invention
will be described below with reference to FIG. 11. In this fourth
embodiment, both the technical ideas of the second and third
embodiments are combined with each other. More specifically, the
feedwater temperature sensor 39 is disposed in the feedwater system
23 as in the second embodiment, and the extraction flowmeter 44 is
disposed in the extraction line 25 as in the third embodiment. With
such an arrangement, the extracted flow controller 40 in this
fourth embodiment performs the control based on the flow rate of
the extracted steam and the control based on the feedwater
temperature. FIG. 12 shows one example of control logic used in
this fourth embodiment. A certain time delay occurs from adjustment
of the extracted flow control valve 38 to actual change of the
feedwater temperature. In this embodiment, therefore, the control
based on the flow rate of the extracted steam is performed with
priority when the flow rate of the extracted steam is fluctuated at
a short cycle, and the control based on the feedwater temperature
is performed with priority when the feedwater temperature continues
to lower or rise for a relatively long time. In practice, as shown
in FIG. 12, the set value of the flow rate of the extracted steam
is determined through the control based on the feedwater
temperature, and the opening command signal 43 for the extracted
flow control valve 38 is outputted based on the difference between
the determined set value and the measured value of the flow rate of
the extracted steam. This fourth embodiment can also provide
similar advantages to those obtainable with the second
embodiment.
Fifth Embodiment
[0082] A boiling water reactor power plant according to still
another embodiment (fifth embodiment) of the present invention will
be described below with reference to FIG. 13.
[0083] In this fifth embodiment, a main steam flowmeter 46 is
disposed in the main steam system 2 between the reactor pressure
vessel 1 and the high pressure turbine 3. If the reactor thermal
power and the flow rate of the main steam are known, the feedwater
temperature is uniquely decided from the heat balance of the
nuclear power plant. Accordingly, measuring the flow rate of the
main steam by the main steam flowmeter 46 disposed in the main
steam system 22, as in this fifth embodiment, is equivalent to the
measurement of the feedwater temperature in the second embodiment.
The arrangement of this fifth embodiment is similar to that of the
second embodiment except that the main steam flowmeter 46 is
disposed instead of the feedwater temperature sensor 39 and the
extracted flow controller 40 controls the extracted flow control
valve 38 in accordance with the measured value from the main steam
flowmeter 46.
[0084] In this embodiment, the extracted flow controller 40
receives a main-steam flow measured value signal 47 outputted from
the main steam flowmeter 46 and a set value signal 48 for the flow
rate of the main steam. Then, the extracted flow controller 40
produces an opening demand signal 43 based on those two signals and
outputs it to the extracted flow control valve 38. If the measured
value of the flow rate of the main steam is smaller than the set
value of the flow rate of the main steam, this means that the
feedwater temperature is too low, namely the flow rate of the
extracted steam is insufficient. Therefore, the extracted flow
controller 40 outputs the opening demand signal 43 to increase the
opening of the extracted flow control valve 38. Conversely, if the
measured value of the flow rate of the main steam is larger than
the set value, this means that the feedwater temperature is too
high, namely the flow rate of the extracted steam is too large.
Therefore, the extracted flow controller 40 outputs the opening
demand signal 43 to reduce the opening of the extracted flow
control valve 38. This fifth embodiment can also provide similar
advantages to those obtainable with the second embodiment.
Sixth Embodiment
[0085] A boiling water reactor power plant according to still
another embodiment (sixth embodiment) of the present invention will
be described below with reference to FIG. 14. In this sixth
embodiment, the technical ideas of the second, third and fifth
embodiments are combined together. More specifically, the feedwater
temperature sensor 39 is disposed in the feedwater system 23 as in
the second embodiment, the extraction flowmeter 44 is disposed in
the extraction line 25 as in the third embodiment, and the main
steam flowmeter 46 is disposed in the main steam system 2 as in the
fifth embodiment. With such an arrangement, the extracted flow
controller 40 in this sixth embodiment performs the control based
on the flow rate of the main steam, the control based on the flow
rate of the extracted steam, and the control based on the feedwater
temperature. FIG. 15 shows one example of control logic used in
this sixth embodiment. A certain time delay occurs from adjustment
of the extracted flow control valve 38 to actual change of the flow
rate of the main steam, and another certain time delay also occurs,
though being shorter than the time delay regarding the flow rate of
the main steam, from adjustment of the extracted flow control valve
38 to actual change of the feedwater temperature. On the other
hand, a time delay from adjustment of the extracted flow control
valve 38 to actual change of the flow rate of the extracted flow is
short. In this embodiment, therefore, the control based on the flow
rate of the extracted steam is performed with priority when the
flow rate of the extracted steam is fluctuated at a short cycle,
and the control based on the feedwater temperature is performed
with priority when the feedwater temperature continues to lower or
rise for a relatively long time. Further, the control based on the
flow rate of the main steam is performed with priority when the
flow rate of the main steam continues to increase or reduce for a
relatively long time. In practice, as shown in FIG. 15, the set
value of the feedwater temperature is determined through control
based on the flow rate of the main steam, and the set value of the
flow rate of the extracted steam is determined based on the
difference between the determined set value and the measured value
of the feedwater temperature. Then, the opening demand signal 43
for the extracted flow control valve 38 is outputted based on the
difference between the determined set value and the measured value
of the flow rate of the extracted steam. This sixth embodiment can
also provide similar advantages to those obtainable with the second
embodiment.
[0086] Instead of the above-described arrangement, the main steam
flowmeter 46 and the feedwater temperature sensor 39 may be
disposed to perform the control based on the flow rate of the main
steam and the control based on the feedwater temperature. Further,
the main steam flowmeter 46 and the extraction flowmeter 44 may be
disposed to perform the control based on the flow rate of the main
steam and the control based on the flow rate of the extracted
steam.
[0087] Generally, when the flow rate of the extracted steam is
reduced to lower the feedwater temperature, the thermal efficiency
of the plant is reduced. In order to suppress such a reduction of
the thermal efficiency, it is preferable to reduce the flow rate of
the steam extracted from the extraction point that is positioned as
close as possible to the uppermost side. Therefore, a greater
effect can be obtained by installing the extracted flow control
valve 38 in the extraction line for extracting the steam from a
point downstream of the inlet of the high pressure turbine and
upstream of the inlet of the lower pressure turbine. While the
extracted flow control valve 38 is disposed only in one extraction
line in the second to sixth embodiments, the feedwater temperature
cannot be sufficiently lowered in some cases by reducing the flow
rate of the extracted steam through only one extraction line. In
such a case, the extracted flow control valve 38 is disposed in
plural extraction lines.
[0088] In the boiling water reactor power plant, as mentioned
above, uprate of the reactor thermal power up to about 102% is
generally feasible just by increasing the measurement accuracy of
the feedwater flowmeter 39, etc., and the feedwater temperature is
not required to be lowered in such an uprate range. In the boiling
water reactor power plant, therefore, the control of the feedwater
temperature described in the second to sixth embodiments is more
effective when applied to the case of uprating the reactor thermal
power in the range of larger than 102%, but smaller than 105%.
Further, at the uprate of the nuclear thermal power in the range of
105% to 120%, substantial change of system equipment, e.g.,
replacement of the high pressure turbine 3, is not required in
general. The effects of those embodiments are especially noticeable
when applied to the uprate of the reactor thermal power in excess
of 105% because the replacement of the high pressure turbine 3 is
not required even in the power uprate operation in excess of 105%
by employing the power uprating method of lowering the feedwater
temperature according to the present invention.
Seventh Embodiment
[0089] While the second to sixth embodiments have been described in
connection with the case where the power uprating method of
lowering the feedwater temperature is applied to the boiling water
reactor power plant, the following description is made of an
example in which the power uprating method is applied to a
pressurized water reactor power plant as one of reactor power
plants.
[0090] The pressurized water reactor power plant according to still
another embodiment (seventh embodiment) of the present invention
will be described below with reference to FIG. 16. Feedwater
temperature control logic used in this seventh embodiment is the
same as that shown in FIG. 9.
[0091] In this seventh embodiment, a steam generator 49 is newly
installed in addition to the construction of the second embodiment
such that a primary loop and a secondary loop are formed. The
primary loop is a circulation loop starting from the reactor
pressure vessel 1, passing the steam generator 49, and returning to
the reactor pressure vessel 1. The secondary loop is formed by
connecting both the main steam system 2 and the feedwater system 23
in the second embodiment to the steam generator 49. The
high-temperature coolant generated from the reactor pressure vessel
1 is supplied to the steam generator 49 and is returned to the
reactor pressure vessel 1 after the coolant temperature has been
lowered. In the steam generator 49, the feedwater supplied from the
feedwater system 23 is heated by the high-temperature coolant to
become steam. The secondary steam delivered from the steam
generator 49 is introduced to the high-pressure turbine 3, the
moisture separator and heater 24, and the low-pressure turbine 5
through the main steam line 2. The steam discharged from the
low-pressure turbine 5 is condensed by the condenser 6 to become
water. This water is fed to the steam generator 49 through the
feedwater system 23 in which the low pressure feedwater heater 7,
the feedwater pump 8, and the high pressure feedwater heater 9 are
disposed. Note that one operation cycle is defined as a period from
startup of the reactor to the time at which the reactor is shut
down for fuel exchange.
[0092] When the reactor thermal power is uprated, the amount of
heat exchange in the steam generator 49 is increased substantially
proportional to the amount of increase of the reactor thermal
power. In order to offset the amount of heat exchange in the steam
generator 49, the flow rate of the feedwater supplied to the steam
generator 49 has to be increased or the enthalpy difference of the
coolant between the inlet and the outlet of the steam generator 49
has to be increased. The known power uprating method employs the
former manner; namely it increases the flow rate of the feedwater
in proportion to the amount of heat exchange in the steam generator
49. On the other hand, this embodiment employs the latter manner,
i.e., the new power uprating method. More specifically, in this
embodiment, increases of both the flow rate of the main steam and
the flow rate of the feedwater in the power uprate operation are
suppressed by intentionally reducing the coolant enthalpy
(temperature) at the inlet of the steam generator 49, to thereby
increase the enthalpy difference between the inlet and the outlet
of the steam generator 49. Thus, this embodiment is adapted for the
new power uprating method and requires additional equipment for
widening a feedwater temperature controllable range so that the
feedwater temperature is lowered to a value beyond the range
estimated in the stage of plant construction.
[0093] The necessity of widening the feedwater temperature
controllable range toward the lower temperature side in turn
requires the flow rate of steam extracted for heating the feedwater
to be reduced in comparison with that before the power uprate. The
extracted steam for heating the feedwater is extracted from the
main steam system 2 including the high pressure turbine 3 and the
low pressure turbine 5, and is introduced to the high pressure
feedwater heater 9 and the low pressure feedwater heater 7 via the
extraction lines 25, 26 and 28, etc. In the pressurized water
reactor power plant of this embodiment, a plurality of main
extraction lines are installed downstream of the inlet of the high
pressure turbine and upstream of the outlet of the low pressure
turbine. To reduce the flow rate of the extracted steam, an
extracted flow control valve 38 is disposed in the extraction line
25 to adjust the flow rate of the extracted steam.
[0094] When the above-mentioned new power uprating method of
increasing the enthalpy difference of the coolant is employed, it
is important that the feedwater temperature be surely lowered to a
preset value. For that reason, as in the second embodiment, a
feedwater temperature sensor 39 is disposed in the feedwater system
23 downstream of the high pressure feedwater heater 9 that is
located most downstream in the feedwater system 23, and the opening
of the extracted flow control valve 38 is controlled to adjust the
flow rate of the extracted steam. The feedwater temperature sensor
39 is disposed in the feedwater system 23 downstream of the high
pressure feedwater heater 9, to which the extracted steam is
supplied at the controlled flow rate, and upstream of the inlet of
the steam generator 28. As an alternative, the feedwater
temperature sensor 39 may be disposed between the high pressure
feedwater heater 9, to which the extracted steam is supplied at the
controlled flow rate, and another suitable feedwater heater
installed downstream of the former. Further, the sensor 39 may be
disposed between an outlet of a high pressure feedwater heater
installed most downstream and an inlet of the steam generator
49.
[0095] One example of control logic executed by the extracted flow
controller 40 in the seventh embodiment will be described below
with reference to FIG. 9. As in the second embodiment, the
extracted flow controller 40 controls the opening of the extracted
flow control valve 38 in accordance with the feedwater temperature
measured value signal 41 and the feedwater temperature set value
signal 42, thereby controlling the flow rate of the extracted steam
for heating the feedwater, which is supplied to the high pressure
feedwater heater 9.
[0096] According to this embodiment, since the feedwater
temperature can be adjusted to the set value through control of the
opening of the extracted flow control valve 38, it is possible to
suppress variations in the amount of power generated during the
power uprate operation of the nuclear power plant.
[0097] Also, according to this embodiment, since the feedwater
temperature can be always held at the set value, it is possible to
suppress the increases of both the flow rate of the main steam and
the flow rate of the feedwater by lowering the feedwater
temperature in the power uprate operation of the reactor. Further,
since the feedwater temperature can be adjusted in real time, the
operation method of this embodiment is adaptable for the load
following operation of the nuclear power plant, as with the second
embodiment, while the flow rate of the main steam and the flow rate
of the feedwater are held constant.
Eighth Embodiment
[0098] A pressurized water reactor power plant according to still
another embodiment (eighth embodiment) of the present invention
will be described below with reference to FIG. 17.
[0099] As in the third embodiment, this eighth embodiment includes,
instead of the feedwater temperature sensor 39, an extraction
flowmeter 44 disposed in the extraction line 25 in which the
extracted flow control valve 38 is disposed. Comparing with the
arrangement of the seventh embodiment that the extracted flow
controller 40 controls the extracted flow control valve 38 in
accordance with the measured value from the feedwater temperature
sensor 39, this eighth embodiment is modified such that the
extracted flow controller 40 controls the extracted flow control
valve 38 in accordance with the measured value from the extraction
flowmeter 44.
[0100] The extracted flow control valve 38 and the extraction
flowmeter 44 may be disposed in the extraction line 25 irrespective
of which one of them is positioned upstream of the other. When the
extraction line 25 is merged midway with another extraction line,
one of the extracted flow control valve 38 and the extraction
flowmeter 44, which is positioned on the downstream side, may be
disposed in the extraction line 25 downstream of the merging point
between the two extraction lines. Also, when the extraction line 25
is branched midway, one of the extracted flow control valve 38 and
the extraction flowmeter 44, which is positioned on the downstream
side, may be disposed in a line after being branched. If the
reactor thermal power, the flow rate of the feedwater, and the flow
rate of the extracted steam are known, the feedwater temperature is
uniquely decided from the heat balance of the nuclear power
plant.
[0101] As in the third embodiment, the extracted flow controller 40
controls the opening of the extracted flow control valve 38 in
accordance with the extracted flow measured value signal 45 and the
extracted flow set value signal 42A. This eighth embodiment can
also provide similar advantages to those obtainable with the
seventh embodiment.
Ninth Embodiment
[0102] A pressurized water reactor power plant according to still
another embodiment (ninth embodiment) of the present invention will
be described below with reference to FIG. 18. In this ninth
embodiment, both the technical ideas of the seventh and eighth
embodiments are combined with each other. More specifically, the
feedwater temperature sensor 39 is disposed in the feedwater system
23 as in the seventh embodiment, and the extraction flowmeter 44 is
disposed in the extraction line 25 as in the eighth embodiment.
With such an arrangement, the extracted flow controller 40 in this
seventh embodiment performs the control based on the flow rate of
the extracted steam and the control based on the feedwater
temperature. Control logic used in this ninth embodiment is the
same as that used in the fourth embodiment and shown in FIG. 12. A
certain time delay occurs from adjustment of the extracted flow
control valve 38 to actual change of the feedwater temperature. In
this embodiment, therefore, the control based on the flow rate of
the extracted steam is performed with priority when the flow rate
of the extracted steam is fluctuated at a short cycle, and the
control based on the feedwater temperature is performed with
priority when the feedwater temperature continues to lower or rise
for a relatively long time. In practice, as shown in FIG. 12, the
set value of the flow rate of the extracted steam is determined
through the control based on the feedwater temperature, and the
opening demand signal 43 for the extracted flow control valve 38 is
outputted based on the difference between the determined set value
and the measured value of the flow rate of the extracted steam.
This ninth embodiment can also provide similar advantages to those
obtainable with the seventh embodiment.
Tenth Embodiment
[0103] A pressurized water reactor power plant according to still
another embodiment (tenth embodiment) of the present invention will
be described below with reference to FIG. 19. This tenth embodiment
employs the main steam flowmeter 46 used in the fifth embodiment.
The main steam flowmeter 46 is disposed in the main steam system 2
downstream of the steam generator 49 and upstream of the inlet of
the high pressure turbine 3. Comparing with the arrangement of the
seventh embodiment that the extracted flow controller 40 controls
the extracted flow control valve 38 in accordance with the measured
value from the feedwater temperature sensor 39, this tenth
embodiment is modified such that the extracted flow controller 40
controls the extracted flow control valve 38 in accordance with the
measured value from the main steam flowmeter 46.
[0104] As in the fifth embodiment, the extracted flow controller 40
receives a main-steam flow measured value signal 47 outputted from
the main steam flowmeter 46 and a set value signal 48 for the flow
rate of the main steam. Then, the extracted flow controller 40
produces an opening demand signal 43 based on those two signals and
controls the extracted flow control valve 38 in accordance with the
produced opening demand signal 43. This tenth embodiment can also
provide similar advantages to those obtainable with the seventh
embodiment.
Eleventh Embodiment
[0105] A pressurized water reactor power plant according to still
another embodiment (eleventh embodiment) of the present invention
will be described below with reference to FIG. 20. In this eleventh
embodiment, the extraction flowmeter 44 and the main steam
flowmeter 46 are added to the arrangement of the seventh
embodiment, as in the sixth embodiment. The extraction flowmeter 44
is disposed in the extraction line 25, and the main steam flowmeter
46 is disposed in the main steam system 2 between the steam
generator 49 and the high pressure turbine 3. With such an
arrangement, the extracted flow controller 40 in this embodiment
performs the control based on the feedwater temperature, the
control based on the flow rate of the main steam, and the control
based on the flow rate of the extracted steam. Control logic used
in this embodiment is the same as that shown in FIG. 15, and the
extracted flow controller 40 executes the control in the same
manner as that in the sixth embodiment. This eleventh embodiment
can also provide similar advantages to those obtainable with the
seventh embodiment.
[0106] Instead of the above-described arrangement, the main steam
flowmeter 46 and the feedwater temperature sensor 39 may be
disposed to perform the control based on the flow rate of the main
steam and the control based on the feedwater temperature. Further,
the main steam flowmeter 46 and the extraction flowmeter 44 may be
disposed to perform the control based on the flow rate of the main
steam and the control based on the flow rate of the extracted
steam.
[0107] While the seventh, eighth and tenth embodiments of the
present invention have been described, by way of example, in
connection with the pressurized water reactor, the present
invention can also be applied to an indirect-cycle plant other than
the pressurized water reactor.
[0108] Generally, when the flow rate of the extracted steam is
reduced to lower the feedwater temperature, the thermal efficiency
of the plant is reduced. In order to suppress such a reduction of
the thermal efficiency, it is preferable to reduce the flow rate of
the steam extracted from the extraction point that is positioned as
possible as close to uppermost side. In the seventh to eleventh
embodiments, therefore, a greater effect can be obtained by
installing the extracted flow control valve 38 in the extraction
line for extracting the steam from a point downstream of the inlet
of the high pressure turbine and upstream of the inlet of the lower
pressure turbine. While the extracted flow control valve 38 is
disposed only in one extraction line in the seventh to eleventh
embodiments, the feedwater temperature cannot be sufficiently
lowered in some cases if the flow rate of the extracted steam
through only one extraction line is reduced. In such a case, the
extracted flow control valve 38 is disposed in plural extraction
lines.
[0109] In the pressurized water reactor power plant, uprate of the
reactor thermal power up to about 102% is generally feasible just
by increasing the measurement accuracy of the feedwater flowmeter
39, etc., and the feedwater temperature is not required to lowered
in such an uprate range, as mentioned above. In the pressurized
water reactor power plant, therefore, the control of the feedwater
temperature described in the seventh to eleventh embodiments is
more effective when applied to the case of uprating the reactor
thermal power in the range of larger than 102%, but smaller than
105%. Further, at the uprate of the nuclear thermal power in the
range of 105% to 120%, substantial change of system equipment,
e.g., replacement of the high pressure turbine 3, is not required
in general. The effects of those embodiments are especially
noticeable when applied to the uprate of the reactor thermal power
in excess of 105% because the replacement of the high pressure
turbine 3 is not required even in the power uprate operation in
excess of 105% by employing the power uprating method of lowering
the feedwater temperature according to the present invention.
* * * * *